The present invention relates to hydraulic control systems for steering and implement actuators for off-highway vehicles, and it more particularly relates to emergency steering operation in case of failure of a steering pump to deliver sufficient fluid power.
In hydraulic control systems for off-highway vehicles having hydraulic steering and hydraulic control of implement, it is desirable to have a standby emergency steering system as is provided by the U.S. Pat. No. 4,190,130, for example, to ensure that the vehicle steering will remain under operator control, at least for a time interval, after failure of a normal hydraulic steering system. This emergency apparatus is normally inactive and serves no useful purpose except under conditions where emergency steering is required, and the normal hydraulic system is used primarily just while the vehicle is in motion.
To make more efficient use of the hydraulic power developed for the steering system, according to the U.S. Pat. No. 4,215,720, a pressure compensator senses the normal hydraulic steering load, and makes any excess fluid power output of a steering pump available for control of an implement. The system according to this patent is primarily for light equipment where a single pump can be used for both implement and steering control, with priority given to steering control to prevent the loss of steering due to implement overload.
An object of the present invention is to provide a hydraulic control system which substantially obviates one or more of the limitations of the described prior art systems.
Another object of the present invention is to provide an efficient hydraulic control system that can be safely used for implement and steering operations on heavy off-highway vehicles.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawing, and in part pointed out as the description of the invention progresses.